Third generation (3G) mobile systems, such as, for instance, universal mobile telecommunication systems (UMTS) standardized within the third generation partnership project (3GPP) have been based on wideband code division multiple access (WCDMA) radio access technology. Today, 3G systems are being deployed on a broad scale all around the world. After enhancing this technology by introducing high-speed downlink packet access (HSDPA) and an enhanced uplink, also referred to as high-speed uplink packet access (HSUPA), the next major step in evolution of the UMTS standard has brought the combination of orthogonal frequency division multiplexing (OFDM) for the downlink and single carrier frequency division multiplexing access (SC-FDMA) for the uplink. This system has been named long term evolution (LTE) since it has been intended to cope with future technology evolutions.
The LTE system represents efficient packet based radio access and radio access networks that provide full IP-based functionalities with low latency and low cost. The downlink will support data modulation schemes QPSK, 16QAM, and 64QAM and the uplink will support QPSK, 16QAM, and at least for some devices also 64QAM, for physical data channel transmissions. The term “downlink” denotes direction from the network to the terminal. The term “uplink” denotes direction from the terminal to the network.
LTE's network access is to be extremely flexible, using a number of defined channel bandwidths between 1.4 and 20 MHz, contrasted with UMTS terrestrial radio access (UTRA) fixed 5 MHz channels. Spectral efficiency is increased by up to four-fold compared with UTRA, and improvements in architecture and signaling reduce round-trip latency. Multiple Input/Multiple Output (MIMO) antenna technology should enable 10 times as many users per cell as 3GPP's original WCDMA radio access technology. To suit as many frequency band allocation arrangements as possible, both paired (frequency division duplex FDD) and unpaired (time division duplex TDD) band operation is supported. LTE can co-exist with earlier 3GPP radio technologies, even in adjacent channels, and calls can be handed over to and from all 3GPP's previous radio access technologies.
An LTE network architecture including network entities and interfaces between them is exemplified in FIG. 1. As can be seen in FIG. 1, the LTE architecture supports interconnection of different radio access networks (RAN) such as UTRAN or GERAN (GSM EDGE Radio Access Network), which are connected to the EPC via the Serving GPRS Support Node (SGSN). In a 3GPP mobile network, the mobile terminal 110 (called User Equipment, UE, or device) is attached to the access network via the Node B (NB) in the UTRAN and via the evolved Node B (eNB) in the E-UTRAN access. The NB and eNB 120 entities are known as base station in other mobile networks. There are two data packet gateways located in the EPS for supporting the UE mobility—Serving Gateway (SGW) 130 and Packet Data Network Gateway 160 (PDN-GW or shortly PGW). Assuming the E-UTRAN access, the eNB entity 120 may be connected through wired lines to one or more SGWs via the S1-U interface (“U” stays for “user plane”) and to the Mobility Management Entity 140 (MME) via the S1-MMME interface. The SGSN 150 and MME 140 are also referred to as serving core network (CN) nodes.
As shown above, the E-UTRAN consists of an eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC) and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated uplink Quality of Service (QoS), cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of downlink/uplink user plane packet headers. The eNodeBs are interconnected with each other by means of the X2 interface.
FIG. 2 illustrates structure of a component carrier in LTE Release 8. The downlink component carrier of the 3GPP LTE Release 8 is sub-divided in the time-frequency domain in so-called subframes each of which is divided into two downlink slots, one of which is shown in FIG. 2 as 220 corresponding to a time period Tslot. The first downlink slot comprises a control channel region within the first OFDM symbol(s). Each sub-frame consists of a given number of OFDM symbols in the time domain, each OFDM symbol spanning over the entire bandwidth of the component carrier.
In particular, the smallest unit of resources that can be assigned by a scheduler is a resource block also called physical resource block (PRB). A PRB 230 is defined as NsymbDL consecutive OFDM symbols in the time domain and NscRB consecutive sub-carriers in the frequency domain. In practice, the downlink resources are assigned in resource block pairs. A resource block pair consists of two resource blocks. It spans NscRB consecutive sub-carriers in the frequency domain and the entire 2·NsymbDL modulation symbols of the sub-frame in the time domain. NsymbDL may be either 6 or 7 resulting in either 12 or 14 OFDM symbols in total. Consequently, a physical resource block 230 consists of NsymbDL×NscRB resource elements corresponding to one slot in the time domain and 180 kHz in the frequency domain (further details on the downlink resource grid can be found, for example, in 3GPP TS 36.211, “Evolved universal terrestrial radio access (E-UTRA); physical channels and modulations (Release 10)”, version 10.4.0, 2012, Section 6.2, freely available at www.3gpp.org, which is incorporated herein by reference). While it can happen that some resource elements within a resource block or resource block pair are not used even though it has been scheduled, for simplicity of the used terminology still the whole resource block or resource block pair is assigned. Examples for resource elements that are actually not assigned by a scheduler include reference signals, broadcast signals, synchronization signals, and resource elements used for various control signal or channel transmissions.
The number of physical resource blocks NRBDL in downlink depends on the downlink transmission bandwidth configured in the cell and is at present defined in LTE as being from the interval of 6 to 110 (P)RBs. It is common practice in LTE to denote the bandwidth either in units of Hz (e.g. 10 MHz) or in units of resource blocks, e.g. for the downlink case the cell bandwidth can equivalently expressed as e.g. 10 MHz or NRBDL=50 RB.
A channel resource may be defined as a “resource block” as exemplary illustrated in FIG. 3 where a multi-carrier communication system, e.g. employing OFDM as for example discussed in the LTE work item of 3GPP, is assumed. More generally, it may be assumed that a resource block designates the smallest resource unit on an air interface of a mobile communication that can be assigned by a scheduler. The dimensions of a resource block may be any combination of time (e.g. time slot, sub-frame, frame, etc. for time division multiplex (TDM)), frequency (e.g. subband, carrier frequency, etc. for frequency division multiplex (FDM)), code (e.g. spreading code for code division multiplex (CDM)), antenna (e.g. Multiple Input Multiple Output (MIMO)), etc. depending on the access scheme used in the mobile communication system.
The data are mapped onto physical resource blocks by means of pairs of virtual resource blocks. A pair of virtual resource blocks is mapped onto a pair of physical resource blocks. The following two types of virtual resource blocks are defined according to their mapping on the physical resource blocks in LTE downlink: Localised Virtual Resource Block (LVRB) and Distributed Virtual Resource Block (DVRB). In the localised transmission mode using the localised VRBs, the eNB has full control which and how many resource blocks are used, and should use this control usually to pick resource blocks that result in a large spectral efficiency. In most mobile communication systems, this results in adjacent physical resource blocks or multiple clusters of adjacent physical resource blocks for the transmission to a single user equipment, because the radio channel is coherent in the frequency domain, implying that if one physical resource block offers a large spectral efficiency, then it is very likely that an adjacent physical resource block offers a similarly large spectral efficiency. In the distributed transmission mode using the distributed VRBs, the physical resource blocks carrying data for the same UE are distributed across the frequency band in order to hit at least some physical resource blocks that offer a sufficiently large spectral efficiency, thereby obtaining frequency diversity.
In 3GPP LTE Release 8 the downlink control signaling is basically carried by the following three physical channels:                Physical control format indicator channel (PCFICH) for indicating the number of OFDM symbols used for control signaling in a sub-frame (i.e. the size of the control channel region);        Physical hybrid ARQ indicator channel (PHICH) for carrying the downlink ACK/NACK associated with uplink data transmission; and        Physical downlink control channel (PDCCH) for carrying downlink scheduling assignments and uplink scheduling assignments.        
The PCFICH is sent from a known position within the control signaling region of a downlink sub-frame using a known pre-defined modulation and coding scheme. The user equipment decodes the PCFICH in order to obtain information about a size of the control signaling region in a sub-frame, for instance, the number of OFDM symbols. If the user equipment (UE) is unable to decode the PCFICH or if it obtains an erroneous PCFICH value, it will not be able to correctly decode the L1/L2 control signaling (PDCCH) comprised in the control signaling region, which may result in losing all resource assignments contained therein.
The PDCCH carries control information, such as, for instance, scheduling grants for allocating resources for downlink or uplink data transmission. The PDCCH for the user equipment is transmitted on the first of either one, two or three OFDM symbols according to PCFICH within a sub-frame.
Physical downlink shared channel (PDSCH) is used to transport user data. PDSCH is mapped to the remaining OFDM symbols within one sub-frame after PDCCH. The PDSCH resources allocated for one UE are in the units of resource block for each sub-frame.
Physical uplink shared channel (PUSCH) carries user data. Physical Uplink Control Channel (PUCCH) carries signaling in the uplink direction such as scheduling requests, HARQ positive and negative acknowledgements in response to data packets on PDSCH, and channel state information (CSI).
FIG. 3 schematically illustrates an example of mapping of data onto a physical channel in LTE. It is noted that this example is a simplified mapping for illustrational purposes only. User data (IP packets) may be generated by the user application. They may include speech, video, text, or any other media possibly compressed and encapsulated into other protocols before forming the IP packets. The IP packets are in EUTRAN further processed on the PDCP layer resulting in addition of a PDCP header. The PDCP packets formed in this manner are further segmented and/or reassembled (reassembling being shown in the figure) into RLC packets to which an RLC header is added. One or more RLC packets are then encapsulated into a MAC packet including also a MAC header and padding, if necessary. The MAC packet is also called “transport block”. Thus, a transport block is from the point of view of the physical layer a packet of user data entering the physical layer. There are predefined transport block sizes (TBS) which may be used in LTE. The transport block is then within one transmission time interval (TTI) mapped onto the subframes on the physical layer (PHY). Details of the mapping of data starting with transport blocks up to the interleaving is shown in FIGS. 5.2.2-1 and 5.3.2-1 and described in the related description of the 3GPP TS 36.212, v.10.4.0, “Evolved universal terrestrial radio access (E-UTRA); Multiplexing and channel coding” available freely at www.3gpp.org and incorporated herein by reference, for the uplink and downlink transmission of user data respectively. Furthermore, the physical channel mapping is described in detail in FIG. 6.3-1 and FIG. 5.3-1 for downlink and uplink, respectively, and the related description in 3GPP TS 36.211, v10.4.0. An functional overview of uplink and downlink shared channel is furthermore given in sections 6.1.1 and 6.2.1 (respectively) of 3GPP TS 36.302, v10.3.0, “Evolved Universal Terrestrial Radio Access (E-UTRA); Services provided by the physical layer”. 
A possibility provided by the LTE in order to improve battery lifetime is the discontinuous transmission (DTX) and reception (DRX). In order to provide a reasonable battery consumption of the terminal (UE), LTE Rel-8/9 as well as Rel-10 provides a concept of discontinuous reception (DRX). Accordingly, the terminal does not have to regularly monitor the control channels but rather can switch off the transmission and the reception over long periods and needs to activate the transceiver only at predefined or required time instances.
The principle of link adaptation is fundamental to the design of a radio interface which is efficient for packet-switched data traffic. Unlike the early versions of UMTS (Universal Mobile Telecommunication System), which used fast closed-loop power control to support circuit-switched services with a roughly constant data rate, link adaptation in LTE adjusts the transmitted data rate (modulation scheme and channel coding rate) dynamically to match the prevailing radio channel capacity for each user.
For the downlink data transmissions in LTE, the eNodeB typically selects the modulation scheme and code rate (MCS) depending on a prediction of the downlink channel conditions. An important input to this selection process is the Channel State Information (CSI) feedback (mentioned above) transmitted by the User Equipment (UE) in the uplink to the eNodeB.
Channel state information is used in a multi-user communication system, such as for example 3GPP LTE to determine the quality of channel resource(s) for one or more users. In general, in response to the CSI feedback the eNodeB can select between QPSK, 16-QAM and 64-QAM schemes and a wide range of code rates. This CSI information may be used to aid in a multi-user scheduling algorithm to assign channel resources to different users, or to adapt link parameters such as modulation scheme, coding rate or transmit power, so as to exploit the assigned channel resources to its fullest potential.
Accordingly, the resource grants are transmitted from the eNodeB to the UE in a downlink control information (DCI) via PDCCH. The downlink control information may be transmitted in different formats, depending on the signaling information necessary. In general, the DCI may include:                a resource block assignment (RBA),        modulation and coding scheme (MCS).        
It may include further information, depending on the signaling information necessary, as also described in Section 9.3.2.3 of the book “LTE: The UMTS Long Term Evolution from theory to practice” by S. Sesia, I. Toufik, M. Baker, April 2009, John Wiley & Sons, ISBN 978-0-470-69716-0, which is incorporated herein by reference. For instance, the DCI may further include HARQ related information such as redundancy version, HARQ process number, or new data indicator; MIMO related information such as pre-coding; power control related information, etc.
The resource block assignment specifies the physical resource blocks which are to be used for the transmission in uplink or downlink.
The modulation and coding scheme defines the modulation scheme employed for the transmission such as QPSK, 16-QAM or 64-QAM. The lower the order of the modulation, the more robust is the transmission. Thus, 64-QAM is typically used when the channel conditions are good. The modulation and coding scheme also defines a code rate for a given modulation. The code rate is chosen depending on the radio link conditions: a lower code rate can be used in poor channel conditions and a higher code rate can be used in the case of good channel conditions. “Good” and “bad” here is used in terms of the signal to noise and interference ratio. The finer adaptation of the code rate is achieved by puncturing or repetition of the generic rate depending on the error correcting coder type.
For uplink resource assignments (for transmissions on the Physical Uplink Shared CHannel (PUSCH)) signaled on PDCCH in LTE, the L1/L2 control information does not contain a HARQ process number, since a synchronous HARQ protocol is employed for LTE uplink. The HARQ process to be used for an uplink transmission is given by the timing. Furthermore it should be noted that the redundancy version (RV) information is jointly encoded with the transport format information, i.e. the RV info is embedded in the transport format (TF) field. The TF respectively modulation and coding scheme (MCS) field has for example a size of bits, which corresponds to 32 entries. 3 TF/MCS table entries are reserved for indicating RVs 1, 2 or 3. The remaining MCS table entries are used to signal the MCS level (TBS) implicitly indicating RV0.
For details on the TBS/RV signaling for uplink assignments on PDCCH please see 3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures”, version 3GPP TS 36.213,v.10.4.0, 2012 (available at http://www.3gpp.org and incorporated herein by reference). The size of the CRC field of the PDCCH is 16 bits.
For downlink assignments (PDSCH) signaled on PDCCH in LTE the Redundancy Version (RV) is signaled separately in a two-bit field. Furthermore the modulation order information is jointly encoded with the transport format information. Similar to the uplink case there is 5 bit MCS field signaled on PDCCH. 3 of the entries are reserved to signal an explicit modulation order, providing no Transport format (Transport block) info. For the remaining 29 entries modulation order and Transport block size info are signaled.
In order to increase frequency diversity, LTE provides a possibility of hopping. Two hopping modes are supported, hopping only between subframes (inter-subframe hopping) and hopping both between and within subframes (inter- and intra-subframe hopping). In case of intrasubframe hopping, a frequency hop occurs at the slot boundary in the middle of the subframe. This provides frequency diversity within a codeword. Inter-subframe hopping provides frequency diversity between HARQ retransmissions of a transport block, as the frequency allocation hops every allocated subframe.
An improvement of Release 11 has been agreed as a study item for standardization and relates to providing low cost machine type communication (MTC) terminals based on LTE. Moreover, LTE RAN enhancements for diverse data applications are under study. The machine type communication traffic profiles include sporadic data access for exchange of relatively small data amounts. Such a type of communication is particularly relevant for applications which require always-on connectivity, such as smart phones, sporadic access for the purpose of checking emails or social network updates. The aim of the working item is to identify and specify mechanisms at the radio access network level that enable enhancing the ability of the LTE to handle diverse traffic profiles. In particular, the aim is to reduce the costs and complexity of terminals in order to extend the battery life. The machine type communication traffic is in general delay insensitive data traffic in which the terminals and/or eNodeB can wait for some time until the data is delivered. Such traffic may be, for instance, the planned data traffic including regular updates such as measurements or other reports. The amount of data exchange is typically rather small and can be delivered in few subframes. For instance, such data may be SMS type messages for controlling or reporting by a machine.
It is suggested that the MTC terminals shall only operate with the 1.4 MHz bandwidth only (or another relatively small bandwidth compared to the current minimum requirement of 20 MHz) and shall be only addressable by E-PDCCH since the PDCCH is incompatible for different bandwidths. Addressing by E-PDCCH means that the DCI is transmitted in the PDSCH region. E-PDCCH is an enhanced PDCCH channel under study for release 11, which should provide more efficient and robust transmission.
The MTC terminals should have a reduced functionality in comparison with LTE terminals. As described above, the MTC terminals may also differ from the other terminal types by the characteristics of its traffic. A traffic model for the MTC traffic is provided in Annex A of 3GPP TR 36.888, v.0.2.0, “Study on provision of low-cost Machine-Type Communications (MTC) User Equipments (UEs) based on LTE”, 2012, freely available at www.3gpp.org in document number R1-120891 and incorporated herein by reference. In particular, the packet sizes of 1000 bits and 10000 bits are considered for evaluation of candidate technologies. Candidate technologies for MTC may be limited to support of QPSK modulation only or in general lower level modulations, reduced number of hybrid ARQ processes or no hybrid ARQ at all, and bandwidth limitations which could however reduce the frequency diversity and therefore affect the coverage.
As can be seen from the above examples, the MTC terminals should have the reduced functionality, which may mainly affect their spectral deficiency. The particularities of the MTC traffic such as transmitting data only at predefined time points and low-power requirements also provide opportunities for considering new and more flexible physical channel mapping strategies.